.composition {
    width: 600px;
    height: 400px;
    position: relative;
    background: url("img/bg.jpg");
}
.comp-item {
    position: absolute;
}

.comp-item.planet-1 {
  top: 23px;
  left: 186px;
  z-index: 1;
}

.comp-item.planet-2 {
  top: 66px;
  left: 51px;
  z-index: 2;
}

.comp-item.planet-3 {
  top: 139px;
  left: 145px;
  z-index: 4;
}

.comp-item.asteroid {
  top: 80px;
  right: 110px;
}

.comp-item.spaceship {
  top: 155px;
  left: 144px;
  z-index: 3;
}

.comp-item.ufo {
  top: 293px;
  left: 117px;
  z-index: 5;
}

.comp-item.superman {
  bottom: 0;
  right: 36px;
}